Preparation and properties of covalently cross-linked sulfonated poly(sulfide sulfone)/polybenzimidazole blend membranes for fuel cell applications

Abstract

To improve the radical oxidative stability, a series of covalently cross-linked blend membranes have been prepared from a sulfonated poly(sulfide sulfone) with 80% degree of sulfonation (SPSSF80) and a polybenzimidazole with pendant amino groups (H2N-PBI) using glycidyloxypropyltrimethoxysilane (KH-560) and bisphenol A diglycidyl ether (BADGE) as cross-linkers. The resulting cross-linked membranes show increased tensile strength but slightly decreased elongation at break compared with the plain SPSSF80. The radical oxidative stability of the blend membranes is significantly improved due to the synergic action of the covalent cross-linking and the presence of the PBI component. For example, the cross-linked membrane with the composition of SPSSF80/H2N-PBI/KH-560 = 7/1/3 started to break into pieces after being soaked in Fenton’s reagent for 98 min, which is about 4 times longer than that (20 min) of the plain SPSSF50 (degree of sulfonation = 50%). The covalent cross-linking is also essential to suppress membrane swelling and to enhance membrane water stability. The KH-560-cross-linked blend membranes tend to show higher proton conductivities at low relative humidities than the BADGE-cross-linked one due to the hydrophilic silica network in the former. At fully hydrated state, the cross-linked membranes generally show high proton conductivities comparable with that of Nafion112®.